Liquid crystal display device and method of manufacturing the same

ABSTRACT

The liquid crystal display device having a mirror function includes a back light assembly, a liquid crystal display panel, a first polarizing plate, a selective reflection polarizing plate and a second polarizing plate. The back light assembly generates a light. The liquid crystal display panel includes an upper substrate, a lower substrate facing the upper substrate, and a liquid crystal layer interposes between the upper substrate and the lower substrate. The liquid crystal display panel receives the light generated from the back light assembly to generate an image. The first polarizing plate is disposed on the upper substrate. The selective reflection polarizing plate is disposed on the first polarizing plate. The selective reflection polarizing plate selectively reflects an external light. The second polarizing plate is disposed on the lower substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relies for priority upon Korean Patent Application No.2003-22999 filed on Apr. 11, 2003, the contents of which are hereinincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device and amethod of manufacturing the liquid crystal display device, and moreparticularly to a liquid crystal display device having a function of amirror and a method of manufacturing the liquid crystal display device.

2. Description of the Related Art

A mirror may be attached on personal information device having a liquidcrystal display device, such as a mobile phone and a personal digitalassistance (PDA).

The mirror may be attached on a flip of the mobile phone or on abackside of a battery of the mobile phone, so that a user does not needa separate mirror. However, the mirror may be broken. Therefore, thepersonal information devices having a mirror function are required.

The general liquid crystal display device uses a liquid crystal displaypanel as a mirror in a reflection mode, and as a display panel in atransmissive mode. However, in a reflection mode, an external lightpasses through a polarizing plate and enters the liquid crystal displaypanel to be reflected. Thus, a reflectivity is lowered. When the liquidcrystal display panel or a back light assembly is used as a mirror, thereflectivity is lower than 10%, so that an image is not clear.

SUMMARY OF THE INVENTION

Accordingly, the present invention is provided to substantially obviateone or more problems due to limitations and disadvantages of the relatedart.

It is a feature of the present invention to provide a liquid crystaldisplay device having a mirror function.

It is a second feature of the present invention to provide a method ofmanufacturing the liquid crystal display device.

The liquid crystal display device includes a back light assembly, aliquid crystal display panel, a first polarizing plate, a selectivereflection polarizing plate and a second polarizing plate. The backlight assembly generates a light. The liquid crystal display panelincludes an upper substrate, a lower substrate facing the uppersubstrate, and a liquid crystal layer is interposed between the uppersubstrate and the lower substrate. The liquid crystal display panelreceives the light generated from the back light assembly to display animage. The first polarizing plate is disposed on the upper substrate.The selective reflection polarizing plate is disposed on the firstpolarizing plate. The selective reflection polarizing plate selectivelyreflects an external light. The second polarizing plate is disposed onthe lower substrate.

The method of manufacturing the liquid crystal display device is asfollows. A liquid crystal display panel including an upper substrate, alower substrate facing the upper substrate, and a liquid crystal layeris interposed between the upper substrate and the lower substrate isformed. A first polarizing plate is attached on the upper substrate. Asecond polarizing plate is attached on the lower substrate. A selectivereflection polarizing plate is attached on the first polarizing plate.The selective reflection polarizing plate selectively reflects anexternal light.

The liquid crystal display device includes the selective reflectionpolarizing plate that is attached on the first polarizing plate. Thus,the liquid crystal display device has a mirror function.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantage points of the presentinvention will become more apparent by describing exemplary embodimentsin detail thereof with reference to the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view showing a liquid crystaldisplay device according to an exemplary embodiment of the presentinvention;

FIG. 2 is an exploded schematic cross-sectional view of a liquid crystaldisplay device of FIG. 1 showing a path of light, when the liquidcrystal display device is used as a mirror; and

FIG. 3 is an exploded schematic cross-sectional view of a liquid crystaldisplay device of FIG. 1 showing a path of light, when the liquidcrystal display device is used as a display device.

DESCRIPTION OF INVENTION

Hereinafter the preferred embodiment of the present invention will bedescribed in detail with reference to the accompanied drawings.

FIG. 1 is a schematic cross-sectional view showing a liquid crystaldisplay device according to an exemplary embodiment of the presentinvention.

Referring to FIG. 1, a liquid crystal display device 1000 according toan exemplary embodiment of the present invention includes a liquidcrystal display panel 460, a back light assembly 900, a selectivereflection polarizing plate 700, a first polarizing plate 100 and asecond polarizing plate 600.

The liquid crystal display panel 460 includes a color filter substrate(or upper substrate) 351, an array substrate (or lower substrate) 352and a liquid crystal layer 400 interposed between the color filtersubstrate 351 and the array substrate 352.

The color filter substrate 351 includes a first transparent substrate200, color filters 450R, 450G and 450B, a black matrix 300, a protectionlayer 420 and a common electrode 430. The color filters 450R, 450G and450B are formed on the first transparent substrate 200. The black matrix300 is formed also on the first transparent substrate 200. The blackmatrix 300 is interposed between the color filters 450R, 450G and 450B.The black matrix 300 masks a light leaked from a space disposed betweenthe color filters. Thus, a general black matrix is formed in atwo-layered structure of a chromium (Cr) layer and a chromium oxide(CrOx) layer or a three-layered structure of a chromium (Cr) layer, achromium nitride (CrNx) layer and a chromium oxide (CrOx) layer. Thegeneral black matrix may comprise carbon black so as to prevent loweringa contrast ratio.

In the liquid crystal display device 1000 according to the embodiment ofthe present invention, the black matrix comprises a metal that has ahigh reflectance such as aluminum (Al), aluminum alloy, chromium (Cr),titanium (Ti) and tantalum (Ta), so as to enhance reflectance.

A photo-resist of a natural protein that may be dyed, such as gelatin orcasein is coated on the color filter substrate. Then, the color filtersubstrate having a mask thereon is exposed and developed. A red-coloredpigment or dyes is added to the natural protein, so that a red colorfilter 450R is formed. A green color filter 450G and a blue color filter450B are formed through the same procedure.

A protection layer 420 is formed on the color filters 450R, 450G and450B. The protection layer 420 may comprise a transparent material suchas acryl resin.

A common electrode 430 is formed on the protection layer. The commonelectrode 430 may comprise an indium tin oxide (ITO) or an indium zincoxide (IZO). The indium tin oxide (ITO) and an indium zinc oxide (IZO)are transparent and electrically conductive. The common electrode 430forms a reference voltage.

The array substrate 352 includes a pixel electrode 440 and a secondtransparent electrode 500. The pixel electrode 440 is arranged in amatrix shape corresponding to the color filters 450R, 450G and 450B. Animage voltage is applied to the pixel electrode to apply an electricfield between the common electrode 430 and the pixel electrode 440.Thus, an arrangement of the liquid crystal molecules is changed tomodulate a transmittance of a light generated from the back lightassembly 900.

The back light assembly 900 is disposed under the array substrate 352.The back light assembly 900 provides the array substrate 352 with light.The back light assembly 900 includes a lamp 110 and a light guide plate460. A first light generated from the lamp 110 is transformed into asecond light that is two-dimensional via the light guide plate 800.

A direct-illumination type liquid crystal display device does not needthe light guide plate 800. A plurality of the lamps 110 is disposeddirectly under the array substrate 352 in the direct-illumination typeliquid crystal display device.

The first polarizing plate 100 is disposed on the first transparentsubstrate 200 of the color filter substrate 351. The second polarizingplate 600 is disposed on the second transparent substrate 500 of thearray substrate 352.

The selective reflection polarizing plate 700 is disposed on the firstpolarizing plate 700. The selective reflection polarizing plate 700reflects a portion of the external light, when the lamp 110 of the backlight assembly 900 is turned off. The portion is above 50%. The firstpolarizing plate 100 absorbs a first portion of light and allows asecond portion of light to pass through the first polarizing plate 100.A polarizing axis of the second portion of the light is substantiallyparallel with a polarizing axis of the first polarizing plate 100.

Thus, the selective reflection polarizing plate 700 may be operated as amirror, and the first polarizing plate is operated as an analyzer so asto display an image generated from the color filter substrate 351.

The polarizing axis of the selective reflection polarizing plate 700 issubstantially parallel with the first polarizing axis of the firstpolarizing plate 100. Thus, the light that passes through the selectivereflection polarizing plate 700 may pass through the first polarizingplate 100 to be reflected on the black matrix 300. The polarizing axisof the light is not changed, so that the light that is reflected on theblack matrix 300 may pass through both the first polarizing plate 100and the selective reflection polarizing plate 700. Thus, the liquidcrystal display device 1000 may be operated as a mirror.

When the liquid crystal display device 1000 displays an image, an imagelight analyzed by the first polarizing plate 100 may pass through theselective reflection polarizing plate 700. Thus, a user may recognizethe image light.

A total reflectance R of the liquid crystal display device 1000 isexpressed as the following expression 1.R=r+r×(1−A),  Expression 1

wherein ‘r’ denotes a reflectance of the selective reflection polarizingplate 700, and ‘A’ denotes an aperture ratio.

For example, when the reflectance ‘r’ of the selective reflectionpolarizing plate 700 is 50%, and the aperture ratio ‘A’ is 0.5, thetotal reflectance ‘R’ of the liquid crystal display device 1000 is 75%.According to the expression 1, the total reflectance of the liquidcrystal display device 1000 may be adjusted.

The second polarizing plate 600 is disposed under the array substrate352. A light that exits from the back light assembly 900 is polarized toform a first light, while passing through the second polarizing plate600. A polarizing axis of the first light is twisted by about 90° toform a second light, while the first light passing through the liquidcrystal layer 400. The second light passes through both of the firstpolarizing plate 100 and the selective reflection polarizing plate 700,so that an image is formed.

The liquid crystal display device 1000 may be a normally black modeliquid crystal display device or a normally white mode liquid crystaldisplay device.

In the normally black mode liquid crystal display device, light may notpass through the liquid crystal display panel of the liquid crystaldisplay device, when no electric fields are applied to liquid crystalmolecules. In the normally white mode liquid crystal display device,light may pass through the liquid crystal display panel of the liquidcrystal display device, when no electric fields are applied to liquidcrystal molecules.

In the normally black mode liquid crystal display device 1000, a secondpolarizing axis of the second polarizing plate 600 is substantiallyparallel to the first polarizing axis of the first polarizing plate 100,and in the normally white mode liquid crystal display device 1000, thesecond polarizing axis of the second polarizing plate 600 issubstantially perpendicular to the first polarizing axis of the firstpolarizing plate 100.

The selective reflecting polarizing plate 700 may be a linear selectivereflecting polarizing plate or a circular selective reflectingpolarizing plate.

For example, a dual brightness enhancement film (DBEF) may be used asthe linear selective reflecting polarizing plate. A cholesteric liquidcrystal polirizer may be used as the circular selective reflectingpolarizing plate.

FIG. 2 is an exploded schematic cross-sectional view of a liquid-crystaldisplay device of FIG. 1 showing a path of light, when the liquidcrystal display device is used as a mirror.

Referring to FIG. 2, when a lamp 110 of a liquid crystal display device1000 is turned off, the liquid crystal display device 1000 may functionas a mirror. A first portion of an external light L1 is reflected on aselective reflection polarizing plate 700, so that the liquid crystaldisplay device 1000 functions as the mirror.

A light is an electromagnetic wave having a specific range ofwavelength. When a direction of an oscillation of the electromagneticwave is isotropic in a direction that is vertical to the advancingdirection of the light, the electromagnetic wave is referred to as anatural light. When a direction of an oscillation of the electromagneticwave is fixed, the electromagnetic wave is referred to as a polarizedlight.

The liquid crystal display device 1000 includes a selective reflectionpolarizing plate 700, a first polarizing plate 100 and a secondpolarizing plate 600.

A first portion of the external light L1 has a different direction ofpolarizing axis with that of the selective reflection polarizing plate700. A second portion of the external light L1 has substantially thesame direction of the polarizing axis as that of the selectivereflection polarizing plate 700.

When the lamp 110 is turned off, the first portion of an external lightL1 that is natural light is reflected on the selective reflectionpolarizing plate 700. The second portion of external light L1 passesthrough the selective reflection polarizing plate 700 to form a secondlight L2. The second light L2 passes though the first polarizing plate100 to form a third light L3, because the selective reflectionpolarizing plate 700 and the first polarizing plate 100 have the samedirection as the polarizing axis. The third light L3 passes through afirst transparent substrate 200 to form a fourth light L4. The fourthlight L4 is reflected on a black matrix 300 and exits from the firsttransparent substrate 200 to form a fifth light L5.

The black matrix 300 comprises a metal that has a high reflectance.Examples of the metal include aluminum (Al), aluminum alloy, chromium(Cr), titanium (Ti), tantalum (Ta), etc. Thus, the fourth light L4 maybe reflected well.

The fifth light L5 passes through the first polarizing plate 100 to forma sixth light L6. The sixth light L6 passes through the selectivereflection polarizing plate 700.

FIG. 3 is an exploded schematic cross-sectional view of a liquid crystaldisplay device of FIG. 1 showing a path of light, when the liquidcrystal display device is used as a display device.

Referring to FIG. 3, when a lamp 110 of a liquid crystal display device1000 is turned on, the liquid crystal display device 1000 displays animage. A light guide plate 800 transforms a one-dimensional lightgenerated from the lamp 110 into a two-dimensional light. Thetwo-dimensional light exits from the light guide plate 800 to form aninth light L9. The ninth light L9 is isotropic in a direction that isvertical to direction of advancing. The ninth light L9 passes through asecond polarizing plate 600, and is polarized to form a tenth light L10.The tenth light L10 enters the liquid crystal display panel 460. Thetenth light L10 includes light of which wavelength is various. Thus, thetenth light L10 has a white color.

When an image voltage is not applied to a pixel electrode 440, apolarizing axis of the tenth light L10 is rotated by about 90° andfiltered to have a specific wavelength by color filters 450R, 450G and450B, so that the tenth light is transformed into an eleventh light L11.Thus, the eleventh light L11 has a red color, a green color or a bluecolor, and the polarizing axis of the eleventh light L11 issubstantially perpendicular to the polarizing axis of the tenth lightL10.

The polarizing axis of the eleventh light L11 is parallel with thepolarizing axis of the first polarizing plate 100, so that the eleventhlight L11 passes through the first polarizing plate 100 to form atwelfth light L12. The twelfth light L12 passes through a selectivereflection polarizing plate 700 to form a thirteenth light L13.

When the image voltage is applied to the pixel electrode 440, liquidcrystal molecules are erected, so that the tenth light L10 passesthrough the liquid crystal display panel 460 without being rotated.Thus, a fourteenth light L14 of which polarizing axis is substantiallyparallel with that of the tenth light L10 exits from the liquid crystaldisplay panel 460. The fourteenth light L14 has a specific color such asa red color, a green color or a blue color.

The fourteenth light L14 may not pass through the first polarizing plate100 because the polarizing axis of the fourteenth light L14 issubstantially perpendicular to that of the first polarizing plate 100.

Thus, a light that exits from each of pixels of the liquid crystaldisplay panel 460 has various color and luminance, so that the liquidcrystal display panel displays an image.

Hereinbefore, a normally white mode liquid crystal display device isexplained for an example. However, the selective reflection polarizingplate may be attached on a normally black mode liquid crystal displaydevice. In normally black mode liquid crystal display device, theselective reflection polarizing plate, the first polarizing plate, andthe second polarizing plate have substantially parallel polarizing axis.

Having described the exemplary embodiments of the present invention andits advantages, it is noted that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by appended claims.

1. A liquid crystal display (LCD) device comprising: a back lightassembly that generates a first light; a liquid crystal display panelincluding an upper substrate, a lower substrate facing the uppersubstrate, and a liquid crystal layer interposed between the uppersubstrate and the lower substrate, the liquid crystal display panelreceiving the first light generated from the back light assembly todisplay an image; a first polarizing plate disposed on the uppersubstrate; a selective reflection polarizing plate disposed on the firstpolarizing plate, the selective reflection polarizing plate reflecting aportion of an external light; and a second polarizing plate disposed onthe lower substrate, wherein the upper substrate includes color filtersarranged in a matrix formation and a black matrix disposed between thecolor filters, wherein the black matrix comprises a material selectedfrom the group consisting of aluminum (Al), aluminum alloy, chromium(Cr), titanium (Ti), tantalum (Ta) and a mixture thereof, and whereinthe black matrix reflects the external light that it receives throughthe selective reflection polarizing plate and the first polarizingplate.
 2. The LCD device of claim 1, wherein the second polarizing platepolarizes the first light generated from the back light assembly, andthe first polarizing plate analyzes a second light that passes throughthe liquid crystal display panel.
 3. The LCD device of claim 1, whereinthe selective reflection polarizing plate reflects a portion of theexternal light, the portion being above 50%. 4-5. (canceled)
 6. The LCDdevice of claim 1, wherein a first polarizing axis of the firstpolarizing plate is substantially parallel to a second polarizing axisof the second polarizing plate.
 7. The LCD device of claim 1, wherein afirst polarizing axis of the first polarizing plate is substantiallyperpendicular to a second polarizing axis of the second polarizingplate.
 8. The LCD of claim 1, wherein a first polarizing axis of thefirst polarizing plate is substantially parallel to a second polarizingaxis of the second polarizing plate.
 9. The LCD device of claim 1,wherein the selective reflection polarizing plate corresponds to alinear selective reflection film.
 10. The LCD device of claim 9, whereinthe linear selective reflection polarizing plate is a dual brightnessenhancement film.
 11. The LCD device of claim 1, wherein the selectivereflection polarizing plate corresponds to a circular selectivereflection film.
 12. The LCD device of claim 11, wherein the circularselective reflection film is a cholesteric liquid crystal polarizer. 13.A method of manufacturing a liquid crystal display device comprising:forming a liquid crystal display panel including an upper substrate, alower substrate facing the upper substrate, and a liquid crystal layerinterposed between the upper substrate and the lower substrate;attaching a first polarizing plate on the upper substrate; attaching asecond polarizing plate on the lower substrate; and attaching aselective reflection polarizing plate on the first polarizing plate, theselective reflection polarizing plate reflecting a portion of anexternal light; wherein the upper substrate includes color filtersarranged in a matrix formation and a black matrix disposed between thecolor filters, wherein the black matrix comprises a material selectedfrom the group consisting of aluminum (Al), aluminum alloy, chromium(Cr), titanium (Ti), tantalum (Ta) and a mixture thereof, and whereinthe black matrix reflects the external light that it receives throughthe selective reflection polarizing plate and the first polarizingplate.
 14. The method of claim 13, wherein the second polarizing platepolarizes a first light generated from the back light assembly, and thefirst polarizing plate analyzes a second light that passes through theliquid crystal display panel.
 15. The method of claim 13, wherein theselective reflection polarizing plate reflects a portion of the externallight, the portion being above 50%. 16-17. (canceled)
 18. The method ofclaim 13, wherein a first polarizing axis of the first polarizing plateis substantially parallel to a polarizing axis of the selectivereflection polarizing plate.
 19. The method of claim 13, wherein a firstpolarizing axis of the first polarizing plate is substantiallyperpendicular to a second polarizing axis of the second polarizingplate.
 20. The method of claim 13, wherein a first polarizing axis ofthe first polarizing plate is substantially parallel to a secondpolarizing axis of the second polarizing plate.
 21. The method of claim13, wherein the selective reflection polarizing plate corresponds to alinear selective reflection film.
 22. The method of claim 21, whereinthe linear selective reflection polarizing plate is a dual brightnessenhancement film.
 23. The method of claim 13, wherein the selectivereflection polarizing plate corresponds to a circular selectivereflection film.
 24. The method of claim 23, wherein the circularselective reflection polarizing plate is a cholesteric liquid crystalpolarizer.